We begin with the United States sending Vladimir Putin of Russia a unmistaken message. Back down. U.s. Troops are being sent for training exercises. Moving closer to the center of the dangerous tug of war that began in Ukraine. ABC's Martha Raddatz tells us what this means for Americans tonight. Martha. Reporter: The us has been watching every move Putin has made since promises less than a week ago from the Russians that they would help calm the situation in Ukraine. Quite the opposite has happened. Now we're moving in those troops as a message Reporter: With tensions rising and the death toll as well. Today marks the most blatant show of U.S. Force since the crisis began. 600 American soldiers will immediately begin deploying to Poland, Lithuania, Latvia and Estonia to conduct boots on the ground infantry exercises in support of those nato allies. A strong message to Russia with Nothing we've seen out of Russia of their armed forces is de-escalating the tension. These exercises were conceived as a result of what's going on in Ukraine. Reporter: At the same time the warship uss Taylor will move into the black sea to replace the destroyer uss Donald cook. This as Putin keeps tens of thousands of his troops along Ukraine's eastern border. Also raising fears that the takeover of crimea might embolden Putin to move into other nations with large ethnic Russia Russians. As many as 100 special forces have crossed into southeastern Ukraine organizing the hostile takeover of government buildings and stirring up pro Russian supporters. All of this prompting vice president Biden who was in Ukraine to warn Putin to get his troops and supporters out of those buildings. We need to see these kind of concrete steps we need to see them without delay. How long do the troops stay there? It's expected the U.S. Will have them in the country until the end of the year. And they could expand to other countries if this escalated. And now return to the latest on the teen-age boy who stowed away next to the wheel of a

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